The present invention relates to an improved self-riveting or self-attaching fastening element, preferably a self-riveting male fastening element such as a stud, bolt or the like, which is permanently attached to a panel in an opening in the panel. More specifically, the present invention relates to a self-riveting fastening element having a tubular riveting portion which is received through an opening in the panel into a concave annular die cavity to permanently rivet the fastening element to the panel.
Self-riveting male fastening elements of the type disclosed herein were first developed by Profit Verbindungstechnik GmbH and Co. KG of Germany, a company related to the assignee of the present application, as disclosed in U.S. Pat. No. 5,092,724. The fastening element includes a tubular or annular piercing and riveting portion or barrel portion which in the preferred embodiment pierced an opening in the panel which is then received through the panel opening into a din member having an annular concave die cavity. The die then deforms the free end of the barrel or riveting portion radially outwardly to permanently attach the fastening element to the panel. The fastening element further includes a radial flange portion which is driven into the panel as the free end of the tubular riveting portion is deformed radially outwardly forming a rigid secure installation in a panel. In the preferred embodiment, the fastening element further includes a male fastening portion integral with the radial flange or body portion coaxially aligned with the tubular riveting portion. Female fastening elements of this type were also developed, wherein the body portion includes an internal thread forming a nut-type fastener. Alternatively, the bore may be smooth to receive a self-rolling or self-tapping screw or bolt.
Self-attaching fastening elements of this type have been used extensively particularly in automotive and other applications requiring a secure rigid installation of a fastening element such as a stud, bolt, or nut in a metal panel or plate including body panels, brackets, structural elements and the like. However, self-piercing fastening elements of this type are generally limited to applications where the metal panel has a thickness generally less than about 2.5 mm or 0.098 inches. In automotive applications for example one problem solved by the self-piercing fastener disclosed in the above-referenced U.S. patent was to permanently attach a fastening element in relatively thin panels having a thickness of about 0.031 inches in a continuous operation. Later, fastening elements of this type were developed for permanent attachment of the fastening elements in relatively thick or heavy gauge metal panels as disclosed, for example, in U.S. Pat. Nos. 4,713,872; 5,237,733; and 5,564,873. In applications requiring the installation of a self-riveting fastening element of this type in heavy gauge metal panels having a thickness ranging from about 0.08 to 0.25 inches or greater, an opening configured to receive the tubular riveting portion of the fastening element is first formed in the panel. The tubular riveting portion of the fastening element is then received through the panel opening into a concave annular die cavity and the fastening element is then driven toward the die member which deforms the free end of the tubular riveting portion radially outwardly, permanently riveting the fastening element to the panel. The fastening element may include a radial flange portion which is driven into the panel to entrap the panel portion adjacent the panel opening and forming a flush mounting as disclosed in U.S. Pat. Nos. 5,237,733 and 5,564,873. Alternatively, the body portion may include a conical surface adjacent the tubular riveting portion forming a press fit as disclosed in U.S. Pat. No. 4,713,872. In the most preferred embodiment, however, the body portion includes a radial flange portion forming a more secure rigid fastener and panel assembly.
There are, however, problems in the installation of a self-riveting fastening element of the type described having a radial flange portion for installation in heavier gauge metal panels, particularly, but not exclusively male self-riveting fastening elements. A male self-riveting fastening element, for example, is driven toward the die member by a plunger having an annular end portion which surrounds the male fastening portion as disclosed in the above-referenced U.S. patents. The annular driving surface of the plunger is driven against an annular surface of the radial flange portion of the body portion of the fastening element which significantly deforms the radial flange portion during installation as shown in FIG. 9, described below, because of the force required for installation. As described in the above-referenced U.S. patents, self-riveting fasteners of this type are normally installed in a die press generating several tons of force and the die press may simultaneously form the plate or panel into a contoured shape. Several tons of force are required first to deform the free end of the tubular riveting or barrel portion radially outwardly in the concave arcuate annular die cavity, because of the extreme frictional resistance and large hoop stresses developed. These forces have been reduced by including an internal conical chamfifer surface on the free end of the self-riveting portion and by friction resistant coatings; however, these approaches have not eliminated this problem. Further, the force required to deform the radial flange portion of the self-riveting fastening element into the panel results in further deformation of the radial flange portion during the final installation of the fastening element in the panel.
During installation of a self-riveting fastening element of the type described above, the radial flange portion is deformed by the driving surface of the plunger or ram toward and into the tubular riveting portion and radially, resulting in resulted in fewer structural integrity of the fastening element and panel assembly. This problem has reduced applications of this type of self-riveting fastening element in heavier gauge metal pads and problems following installation. As set forth below, this problem has been solved by the improved self-attaching fastening element of this invention by reducing the force required to install the self-riveting fastening element in a panel, thereby reducing the deformation of the radial flange portion during installation.
As described above, the improved self-riveting fastening element of this invention is designed for permanent attachment to a metal panel or plate within a panel opening by a die member having an annular concave die cavity. The self-riveting fastening element includes a tubular riveting portion having generally cylindrical internal and external surfaces and a free end. The self-riveting fastening element further includes a radial flange portion integral with the tubular riveting portion opposite the free end having a diameter greater than the tubular barrel portion and adapted to be driven into the panel as the tubular riveting portion is driven through the panel opening into the annular die cavity. Where the self-riveting fastening element is a male fastening element, the radial flange portion forms part of a body portion of the fastening element, which bridges the tubular riveting portion and closes the end of the tubular barrel portion opposite the free end and a male fastening portion such as a stud or bolt is integral with the flange or body portion opposite the tubular riveting portion and preferably coaxially aligned with the tubular riveting portion. An annular drive surface is thus defined around the male fastening portion. Where the self-riveting fastening element is installed in a preformed opening, as will be required for installation in heavier gauge panels, the tubular riveting portion is first aligned with the panel opening, then driven through the panel opening by a plunger into an annular concave die cavity of a die member. The die member then deforms the free end of the tubular riveting portion radially outwardly preferably in a hook or U-shape and the radial flange portion is simultaneously driven into the panel entrapping the panel metal between the radially deformed hook-shaped riveting portion and the flange portion, forming a secured fastening element and panel assembly.
The force required to deform the free end of the tubular riveting portion in the concave die cavity is significantly reduced by reducing the thickness of the tubular riveting portion adjacent the free end, wherein the internal and external surfaces of the generally cylindrical tubular barrel portion are slightly inclined toward the radial flange portion, such that the thickness of the tubular riveting portion uniformly increases from the free end toward the radial flange portion. In the most preferred embodiment of the self-riveting fastening element of this invention, the internal surface of the tubular riveting portion is cylindrical and parallel to the longitudinal axis of the tubular riveting portion and the external surface is sonically tapered toward the free end of the riveting portion. Most preferably, the free end of the tubular riveting portion includes an outer arcuate surface which smoothly blends into the conical external surface providing a smooth transition from the arcuate outer surface into the conical external surface. The cone angle of the external surface is between about one and five degrees or most preferably between two and three degrees. As described more fully below, this relatively simple modification of the tubular riveting portion results in a significant reduction in the force required to deform the free end of the tubular riveting portion radially outwardly of greater than ten percent. The reduction is force required is achieved without significantly reducing the strength of the deformed hook-shaped free end of the tubular riveting portion.
The force required to drive the radial flange portion of the self-riveting fastening of this invention into the panel is reduced by providing a plurality of arcuate radially inwardly concave surfaces on the radially outer or exterior surface of the radial flange portion. This modification reduces the area of the radial flange portion driven into the panel adjacent the opening and further increases the torque required to turn the self-riveting fastening element relative to the panel following installation. Torque resistance is also an important feature of a self-riveting fastening element of the type described herein because the fastening element is utilized to attach a second element to the fastening element and panel assembly. For example, the self-riveting male fastening element of this invention may include an integral threaded bolt portion which extends from the panel. The bolt is then used to attach an automotive component, for example, to the fastening element and panel assembly which is secured in place by a conventional nut. During the engagement of the nut, however, the bolt may be subject to twisting forces, particularly where the nut is cross-threaded or a thread forming nut or bolt is used and a torque wrench is used. The fastening portion may therefore be subject to substantial tensional loads and must be able to withstand turning of the fastening element relative to the panel following installation. In the most preferred embodiment of the self-riveting fastening element, the radial flange portion is generally polygonal having, for example, six or eight sides. The radially inwardly concave surfaces are defined in the side surfaces of the polygonal radial flange portion located between the points or edges. In the most preferred embodiment, the xe2x80x9cedgesxe2x80x9d of the polygonal radial flange portion include a thin convex arcuate surface and the radially inwardly concave surfaces are located between the thin convex arcuate surfaces of the edges. The radially inwardly concave surfaces between the concave arcuate surfaces most preferably have a relatively large radius. The radius of curvature of the concave arcuate surfaces is defined such that the arc is spaced from the external surface of the tubular riveting portion. In the most preferred embodiment, the radius of the arcuate radially inwardly concave surface is greater than the radius of the external surface of the tubular riveting portion.
Other advantages and meritorious features of the self-riveting fastening element of this invention and method of installation will be more fully understood from the following description of the preferred embodiments, the claims and the appended drawings a brief description of which follows.